Donald Trump’s frustration was clear when he was asked who had approved a pause on sending weapons to Ukraine during a cabinet meeting on Tuesday.

“I don’t know,” he snapped at the reporter. “Why don’t you tell me?”

The freeze in military aid last week blindsided top national security figures, alarmed key allies and was rapidly reversed by the US president himself, but not before generating a rush of headlines about dysfunction and incoherence in the policy process.

At the centre of it all is a little-known Pentagon official: Elbridge Colby, a national security policy chief, who reportedly halted supplies because US stockpiles were running low.

Insiders say, at best, it illustrates confusion about how to put Mr Trump’s “America First” policies into practice and, at worst, it shows how the administration’s decision-making process has broken down.

A former member of the US national security council said Mr Colby had come unstuck because he was trying to put proverbial flesh on the bones of Mr Trump’s vague platform of ending foreign wars and avoiding anything that looked like intervention.

“I don’t think he’s trying anything he didn’t think is the position of the president or the defence secretary. He’s not freelancing,” he said. “He thinks this is the position of the people above him.”